the branding USE flag control that (like other packages).
if you set -branding in make.conf or package.use and re-emerge you should get the vanilla splash. But tbf I likle the gentoo branding._________________The best argument against democracy is a five-minute conversation with the average voter
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If I understand correctly the bug is still open .... I wrote a patch and now compiles with no brand on both x82 and on x64 architectures. I tried compiling on various computers (5), and on all the brand is gone. For me, you can close the post.

The proper fix is to alter the USE flags as advised. However...given that libreoffice on some systems takes a ridiculous amount of time to compile (11 hours on my netbook, for example) it would be massive overkill to edit the USE flags and re-emerge libreoffice just to fix the branding! The startup banner is an ordinary, easily editable png file at:

Code:

/usr/lib64/libreoffice/program/intro.png

...and this can simply be edited or replaced with a different image (there are lots of libreoffice banners available for download online). Even without the "branding" USE flag, you might prefer another image to the default libreoffice logo. In any case, while it makes sense to re-emerge the package to test the effectiveness of the USE flag change on some systems that can build libreoffice quickly, on others it makes more sense just to fix the startup banner and wait for the next version upgrade to have the new USE flag take effect. It's also possible to start libreoffice (or its executables like lowriter) with "--nologo" in order to avoid the splash screen completely.